sortedLastIndexBy (Lodash compatibility)

Implement binary search and transformation function directly

This sortedLastIndexBy function operates slowly due to complex iteratee handling and type conversion.

Instead, implement faster, more modern binary search and transformation functions directly.

Finds the highest index at which a value should be inserted into a sorted array after applying a transformation function.

const index = sortedLastIndexBy(array, value, iteratee);

Reference

sortedLastIndexBy(array, value, iteratee)

Use sortedLastIndexBy to find the highest insertion position of a value in a sorted array after applying a transformation function. When duplicate values exist, it returns the index after the last value.

import { sortedLastIndexBy } from 'es-toolkit/compat';

// Find last insertion position in object array sorted by property
const objects = [{ x: 4 }, { x: 5 }, { x: 5 }];
sortedLastIndexBy(objects, { x: 5 }, 'x');
// Returns 3 (position after the last x: 5)

// Transform using function
const numbers = [10, 20, 20, 30];
sortedLastIndexBy(numbers, 20, n => n);
// Returns 3

For null or undefined arrays, returns 0.

import { sortedLastIndexBy } from 'es-toolkit/compat';

sortedLastIndexBy(null, { x: 1 }, 'x'); // 0
sortedLastIndexBy(undefined, { x: 1 }, 'x'); // 0

Parameters

• array (ArrayLike<T> | null | undefined): The sorted array. Using an unsorted array can produce incorrect results.
• value (T): The value to insert.
• iteratee (optional): The transformation function, property name, or property-value array to apply to each element and value.

Returns

(number): Returns the highest index to insert the value. If the array is null or undefined, returns 0.